Method for continuously producing thermally-stable nitrided manganese



1958 E. M. WANAMAKER ET AL 2,860,080

METHOD FOR commuousw PRODUCING THERMALLY-STABLE NITRIDED MANGANESE Filed June 6, 1956 I 5 Sheets-Sheet 1 r I i him m m (D INVENTORS ELMER M.WANAMAKER DUNCAN D. FORBES a; Pith awn.

ATTORNEYS Nov. 11, 1958 E. M. WANAMAKER ET AL 2,860,080 METHOD FOR CONTINUOUSLY PRODUCING THERMALLY-STABLE' NITRIDED MANGANESE Filed June 6, 1956 5 Sheets-Sheet 2 m m E INVENTORS ELMER M.WANAMAKER DUNCAN D. FORBES QM; 83L m MMVEA ATTORNEYS Nov. 11, 1958 E M. WANAMAKER ETAL METHOD FOR CONTINUOUSLY PRODUCING THERMALLY-STABLE NITRIDED MANGANESE Filed June 6, 1956 5 SheetsSheet s INVENTORS ELMER M.WANAMAKER BY DUNCAN 0. FORBES ATTORN EYS Nov. 11, 1958 E. M. WANAMAKER ETAL 2,360,080

METHOD FOR CONTINUOUSLY PRODUCING THERMALLY-STABLE NITRIDED MANGANESE Filed June 6, 1956 5 Sheets-Sheet 4 FIG. 5'

' INVENTORS ELMER M. WANAMAKER BY DUNCAN D. FORBES PM"; aw twg lm u ATTORNEYS 1958 E. M. WANAMAKER ETAL METHOD FOR commuousur PRODUCING THERMALLY-STABLE NITRIDED MANGANESE 5 Sheets-Sheet 5 Filed June 6, 1956 m IVNVENTORS ELMER M. WANAMAKER BY DUNCAN 0. FORBES ATTORNEYS United States Patent METHOD FOR CONTINUOUSLY PRODUCING THERMALLY STABLE NITRIDED MAN- GANESE Elmer M. Wanamaker and Duncan D. Forbes, Knoxville,

Tenn., assignors to Foote Mineral Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 6, 1956, SerialNo. 589,769

8 Claims. (Cl. 148-431) This invention relates to treating metals with gases, and particularly relates to nitriding metals such as manganese, especially electrolytic manganese. An object of the invention is to provide a continuous process for treating metals with gases, which can be used with particular advantage for producing thermally-stable nitrided electrolytic manganese; and a further object of the invenion is to provide an improved apparatus for use in treating metals with gases.

The exhaustive investigation which culminated in the development of nitrogen-bearing stainless steels capable of withstanding severely corrosive conditions at high temperatures, as described in the United States Patent to Tanczyn No. 2,696,433, demonstrated the utility and advantages of preparing such steels with nitrided electrolytic manganese. The wide variation in the thermal stability of'the different nitrides of manganese poses several practical difliculties in the production of nitrogen-bearing steels, for it has been observed that certain unstable manganese nitrides decompose rapidly at melt temperatures to volatile nitrogen, thereby causing loss of nitrogen and sometimes spattering of the melt. Although the surface hardness properties of these rustless steels increase with higher quantities of nitrogen in the steel, the thermal instability of those manganese nitrides containing from 10% to by weight of nitrogen renders them unsuitable for incorporation in the steel bath. The production of nitrogen-bearing corrosion resistant steels having desirable surface hardness properties thus requires that the thermally-stable nitrides of manganese be used in their preparation.

The present invention provides a continuous process for treating metals with gases, which is especially suitable for producing thermally-stable nitrided manganese con taining up to about 6% by Weight of nitrogen. We have discovered that continuous heating of manganese in contact with a countercurrent stream of gaseous nitrogen in a rotary nitriding vessel effects substantially complete nitriding of the manganese while concomitantly removing substantially all of the hydrogen dissolved in the metal. We have further found that when the vessel is continuously rotated during the heating of the manganese in contact with the gaseous nitrogen, the metal is substantially precluded from fusing or sintering during passage through the vessel. Slow tempering of the hot nitrided manganese under a blanket of gaseous nitrogen has also been found to be requisite to prevent the hot nitrided metal from reacting with oxygen or moisture to form manganese oxides, which is accompanied by denitriding of the metal as a consequence.

Based on these discoveries, the invention provides a continuous process for producing thermally-stable nitrided manganese (or other product) which comprises feeding subdivided solid manganese (or other metal, e g. iron, nickel, cobalt, or chromium) into a rotary vessel, introducing and maintaining a stream of gaseous nitrogen (or other gas) flowing through the vessel at a slightly superatmospheric pressure, continuously rotating the ves- 2,860,080 Patented Nov. 1 1, 1958 ice during which the material being treated is heated in contact with the gaseous nitrogen provides an efiective method for controlling the nitrogen content of the resultant nitrided product.

-The invention also provides improved apparatus for continuously treating manganese or othermetal with nitrogen or other gas. The apparatus is a substantially gas-tightrotary tube furnace comprising an elongated horizontally-inclined rotatable cylindrical furnace tube secured at one end to a non-rotatable'charging device and at the other end to a non-rotatable discharge chute. The furnace tube is provided with'heating means for heating a reaction zone,-and with cooling means for cool ing a tempering zone. Means are provided for holding the charging'device and discharge chute in axially-fixed substantially gas-tight relation to the furnace tube. The

for maintaining the non-rotatable charging device in an.

operative axially-fixed relation with the rotatable furnace tube. Important features of the new apparatus reside in the means'that are provided to secure maximum output from the highly heated reaction zone while maintaining the physical dimensions of this zone as small as possible. One such means is the provision of a preheating zone, adjacent the reaction zone on the side toward the feed end of the furnace, where the incoming metal is heated by conduction along the furnace tube walls and by the hot gases flowing from the reaction zone. Other such means include the provisions that are made to build up and retain a deep bed of material in the preheating and reaction zones, whereby a high rate of feed through the furnace tube is achieved along with an adequate time of retention of material in the reaction zone.

Preferred embodiments of the invention are describedbelow with reference to the accompanying drawings, in which Fig. l-A is an elevation, partly in section, of a portion of the rotary tube furnace of the invention, showing the gas-tight charging'device inoperative combination with the feed end of the furnace tube and showing the preheating zone and the heated reaction. section of the furnace tube;

i Fig. l-B is substantially a continuation of Fig. 1-A and is an elevation, partly in section, of the remaining portion of the rotary tube furnace of the invention, showing the cooled tempering section of the furnace tube and vention, showing how it is mounted in axially-fixed relation with the feed end of the furnace tube; Fig. 5 isan end view, partly in section, of'the char'ging device shown in Fig. 4; Fig, 6 'iswan, elevation, partly in'section and'on an en larged scale, of the gas-tight discharge chute, showing how it is mounted in axially-fixed relation with the discharge end of the furnace tube; and

:Fig. 7 isan end view,-partly in section, of the discharge chute shownin Fig. 6.

Referring to Figs. l-A and'l-B of the drawings, the nitriding'apparatus of this invention comprises a rotary furnace tube 8 having a feed end 9, a preheating zone 10, a heated reaction zone 11, a cooled tempering zone 12, and a discharge end 13. The furnace tube is rotatably mounted on trunnion rollers 14, which are journaled in brackets 15 mounted on supporting columns 16. The entire structure 'rests on a frame comprising a pan of beams 17 extending the length of the apparatus and resting pivotally at one end on a bearing 18 and supported intermediately and at the other end by adjustable jacks 19. By manipulation of the jacks, the supporting structure may be adjustably inclined, within limits, to any desired horizontal slope.

sThe trunnion rollers 14 engage bearing rings 20 welded to the furnace tube 8. One end of the furnace tube 8 is provided with an annular sprocket collar 21 driven by a sprocket chain 22 from sprocket wheel 23, which in turn is driven by a motor 24 through speed reduction mechanism indicated generally at 25. By means of the speed reduction mechanism 25, the rate of rotation of the furnace tube 8 may be increased or decreased. The direction of rotation is as schematically indicated in Fig. 3. One bearing ring 20 engages two thrust trunnions 14a (see Fig; 6) at its edges, thus restraining the rotating furnace element against longitudinal movement at this point.

The reaction zone 11 is adjacent to the preheating zone 10 and is completely surrounded by an electrical resistance heating furnace 26. Heat losses from the furnace are minimized by a thick layer of insulation 27; and the whole furnace assembly is enclosed by a furnace shell 28 and is supported on the beams 17. Thermocouples 29 and power leads 30 for various sections of the furnace extend through the furnace shell at strategic locations to provide for close control of the temperatures in the reac tion zone 11. (While electrical heating of the react1on zone is preferred, it is of course apparent that any other desired heating means may be provided.)

The tempering zone 12 is adjacent to the discharge end 13 of the furnace tube 8 and is cooled by water delivered from spray pipes 31. Spent cooling water is collected in a trough 32 supported beneath the tempering zone 12 of the furnace tube on legs 33, which in turn are carried by the beams 17. Water is withdrawn from the trough 32 through a drain pipe 34.

The heated reaction section of the furnace tube should be fabricated of a heat-resistant alloy such as a chromenickel alloy, and for reasons of economy the preheating section and the cooled tempering section are of an ordinary lowor medium-carbonsteel. The three sections are bolted together at flanged joints 9a. In order to increase the time of retention of manganese in the reaction zone, a barrier ring 9b is advantageously interposed between the reaction zone and the tempering zone. In the drawings this ring is shown as being in the form of a truncated cone having an annular flange which is bolted between the two sections of the furnace tube at the flanged joint 9a between the reaction zone 11 and the cooled tempering section 12. The barrier ring is arranged with its apex toward the tempering section of the furnace, so as to avoid a dead space at the outlet from the reaction zone.

10 of the rotatable furnace tube 8 by sealing means indicated at 38 (Figs. 1-A and 4). The charging device can be moved ,back and forth'on a dolly'. 37, whichin'des on rails 43, so that expansion and contraction of the furnace tube .8 may be accommodated without disturbing the The non-rotatable charging device, indicated generally at 36, is secured in axially-fixed relation to the feed end' axially-fixed relation of the charging device .36 to .the furnace tube 8.

The furnace tube 8 is fitted with a closure ring 39 secured to the inner circumference of the furnace tube at its feed end 9; and it also is provided with a plurality of helical conveyor flights 42 mounted immediately adjacent to the closure ring 39 and tightly fitted to the inner circumference of the furnace tube. The conveyor flights are pitched in the direction to advance material delivered through the closure ring into the interior of the furnace at a faster rate than would otherwise obtain due to the slope and rotational speed of the furnace tube. The closure ring 39 and the conveyor flights 42 cooperate to prevent material delivered into the feed end of the furnace tube from spilling out backwards, or from backing up into and choking the feed device, rather than advancing in the intended direction. The flights 42 extend only a short distance into the furnace tube from its feed end, so as to release the feed and build up and maintain a deep bed in the reaction zone of the furnace.

A feeding chute 40 is provided for feeding manganese metal into the furnace tube. The lower end of the feeding chute comprises a sloping feeding conduit 44 which terminates at its lower end in an annular rim 41, the outside diameter of which is only slightlyless than the inside diameter of the closure ring 39. The annular rim 41 extends concentrically into the closure ring 39,-so that manganese introduced into the feeding chute 40 passes through the feeding conduit 44 into the feed end f the furnace tube 8, and is rapidly conveyed further into the furnace by the helical conveyor flights 42. The inside dimensions and slope of the chute 40. and the conduit 44 must be sufiiciently great to permit free flow of the feed stream, with due consideration of its quantity and the shape and size of the individual pieces, without bridging.

The feeding chute 44 is securely enclosed in a housing 45. The housing 45 is provided with observation ports 47 for viewing the operation of the furnace at its charging end. The housing includes a short tubular section 48 which surrounds the feed end of the furnace tube. An annular bellows plate 49 is securely attached to the free end of the housing section 48. A trap door Sit-is, provided at the base of the housing for removing what manganese dust works its way out through the small annular clearance between the feeding conduit rirn 41 and the closure ring 39.

The means 33 by which the housing 45 is sealed inaxially-fixed relation to the furnace tube 8 comprises a bellows 51 fastened at one end in gas-tight relation to the bellows plate 49,. and similarly fastened at the other end to an annular bellows seal plate 52. An annular flange 53 is welded in gas-tight relation to the furnace tube 8. The face of the flange which is adjacent the bellows seal plate constitutes a sealing face, and the opposite face thereof cooperates with an annular guard ring 54 to define an annular yoke channel 55. Surrounding this channel is a yoke ring 56. Yoke fingers (preferably three in number) which carry yoke rollers 57 extend radiaily inwardly from the ring 56 and engage with the walls of the channel 55. The ring as is rigidly fastenedby connecting rods 58 (also preferably three in number) to the bellows plate 49 and thereby to the housing 45. Thus when the furnace tube 8 expands or contracts (it is shown in contracted form in the drawings), the housing 45 and the charging device which it encloses is moved back or forth on the dolly rails 43, the force for moving it being transmitted from the furnace tube through the yoke rollers 57 and the yoke ring and through the connecting rods 58.

Fastened to the bellows plate 49 intermediate the connecting rods are a series of guide rods 59. Comprcssion springs 60 surround these rods and bear against the be'lows seal plate 52, urging it toward'the sealing face of the flange 53. A collar 61 on each guide red 59 receivesthe reaction thrust exerted bythe spring 66. A

packing ring is fast'ened to-the=bellows seal plate'52 and of the furnace.

provides a rotary gas-tight seal against the .face of the flange 53. Lubricant is applied to the sealing face of the packing ring.

The feeding chute 40-receives manganese chips through a double hopper valve 62 mounted above and securely attached to the housing 45. This valve 62 is operated by a motor-driven cam 63 which periodically engages first an upper follower 64, opening the upper valve 65, and then the lower follower 66, thereby opening the lower valve 67; before either valve is opened, the other is snapped closed by one of the valve-closing springs 65a and 67a respectively. A measured continuous stream of manganese is introduced into the furnace by delivering it through a feed chute 68 communicating with the double valve 62. The double valve constitutes a gas lock which minimizes loss of gas as metal is charged more or less continuously into the furnace.

At the discharge end 13 of the furnace tube 8, a nonrotatable discharge chute assembly 70 is mounted in axially-fixed relation therewith. As shown in Figs. 6 and 7, this assembly comprises two discharge chutes 71 and 72. A swivel-mounted deflecting plate 73 actuated by a solenoid 74 deflects the product emerging from the furnace tube down one or the other of these chutes. When the solenoid armature is raised as shown in Fig. 7, the deflecting plate is held by its operating lever 75 and connecting link 76 in the position shown in solid lines to deflect material discharged from the furnace tube into the left-hand chute 72. When the solenoid armature is drawn down by energizing the solenoid, the lever 75 moves to rock the plate 73 about its pivot axis 77 to the position shown in dotted lines to deflect the discharged material into the right-hand chute. Upon de-energizing the solenoid, a tension spring 78 acting through a lever 79 serves to return the deflecting plate to the position shown in solid lines.

Each of the discharge chutes 71 and 72 may be closed off by a door 30 and 81, respectively. Each of these doors is carried by an arm Sila, 8111 which is pivotally mounted on an axis 80b, 81b and is connected to an operating handle 80c, 810. The doors are opened or closed by manipulation of these handles.

The discharge chutes are enclosed in a housing 82 to which plastic or rubber drurn seals 83 are attached beneath each of the chutes 71 and 72. Receptacles 84 and 85, resting on conveyor rollers 86, are placed immediately below these chutes 71 and 72 and sealed in gas-tight relation to the housing by the plastic drum seals. Each of the receptacles 84 and 85 may be separately disengaged from the discharge chute without breaking the gastight seal by first closing the appropriate door 80 or 81.

The discharge chute housing is provided with a viewing port 82a to permit observation of the interior of the furnace and the product discharging from the end of the furnace tube.

The discharge chute housing 82 includes a tubular section 82b which surrounds the discharge end 13 of the furnace tube and is secured to a bellows plate 87. The discharge chute housing is sealed in substantially gastight relation to the furnace tube by a bellows seal of the same general design as that employed at the charging end The seal comprises a bellows 87a secured at one end to the bellows plate 87 and at the other end to a sealing plate 87b. An annular flange 88 is welded to the furnace tube 8. Guide rods 89 are fastened to the bellows plate 87 and carry compression springs 8% which urge the sealing plate toward the flange 88. Collars 90 on the guide rods receive the reaction thrust exerted by the springs 8%. A seal ring 91 fastened to the sealing plate 87b is interposed between the flange 88 and the sealing plate 87b to minimize wear on the sealing surfaces of these members. Lubricant is applied to the sealing faceof the seal ring 91. Since little or no expansion or contraction of the discharge end portion of the furnace tube occurs in normal use, no special 6 means. are needed to permit axial motion of the discharge chute housing.

Nitrogen gas is admitted to the furnace tube through an inlet pipe '92, controlled by a valve 93, connected to the discharge chute housing. Excess gas escapes from the apparatus through a gas outlet conduit 94, connected to the charging device housing, and advantageously extending to below the surface of water in a vessel provided for the purpose, so as to maintain a slight positive pressure (several inches of water) of gas in the furnace tube. Some gas, of course, escapes through the double valve 62 as new manganese is charged into the furnace.

In accordance with the process of the invention, as it is applied to the production of nitrided electrolytic manganese metal, a stream of gaseous nitrogen is continuously introduced into the furnace tube 8 through the gas inlet valve 93 and excess gas escapes from the furnace tube through the gas outlet 94. The pressure of the gaseous nitrogen stream within the furnace tube is maintained slightly above atmospheric pressure, preferably at from 0.1 to 6 inches of water, to exclude foreign gasesfrom the furnace.

Although the nitrogen may be prepared in various ways, as by the thermal decomposition of anhydrous ammonia, we have found thatthe generation of the gaseous nitrogen by combustion of natural gas in air, followed by removal of the carbon dioxide, carbon monoxide and water, provides an inexpensive and very satisfactory source of dry nitrogen free from contaminants.

Electrolytic manganese chips are continuously dropped into the feed chute 68. At regular intervals the upper valve 65 opens, drops a charge of manganese chips to the lower valve 67, and then closes. Then the lower valve opens, dropping the chips into the feeding chute 40 without appreciably lowering the pressure of the gaseous nitrogen stream maintained in the furnace. The manganese charge drops through the feeding conduit 44 and is deflected into the feed end 9 of the furnace tube 8.

There it is rapidly carried further into the furnace and prevented from backing out by the helical flights 42, which thus establish and maintain a deep bed of chips in the prethe length of the tempering zone 12, by the barrier ring Continuous rotation of the furnace tube advances the manganese countercurrently to the gaseous nitrogen stream into and through the reaction zone 11. action zone -is heated and maintained at about 1750 to 1 950 F. by the heating means 26. By continuously rotating the furnace tube 8, the manganese chips are tumbled and thoroughly agitated during passage through the heated reaction zone 11. This agitation not only prevents fusion or sintering of the metal at this high temperature, but insures a uniform diffusion of gaseous nitrogen throughout the entire manganese charge. We have found that substantially all of the hydrogen present in the electrolytic manganese is removed during the agitation of the manganese in the preheating zone 10 and in the first part of the reaction zone 11, while the metal is being raised to the reaction temperature, and is swept out of the furnace by the countercurrent stream of gaseous nitrogen.

By varying the time of retention of the metal in the heated reactionzone 11 in contact with the countercurrent stream of gaseous nitrogen, and controlling the temperature to within the stated range, the completeness of nitriding may be carefully regulated to produce a thermally-stable uniformly nitrided electrolytic manganese containing up to about 6% by weight of nitrogen. The nitrogen content of the finished product is most readily varied by varying the rate of progression of the metal through the reactionzone; and by this means the maximum output of product is achieved for each par The reticular nitrogen content in the product. As an example i of the method, the retention of electrolytic manganese chips for about 1 /2 hours in the heated reaction zone. 11 at 1800" to 1850 F. resulted in producing a thermallystable uniform nitrided electrolytic manganese containing from 4% to 5% by weight of nitrogen, completely free of hydrogen. In another specific example, a 3-hour retention period of the electrolytic manganese chips in the heated reaction zone, maintained at a temperature of 1800 to 1850 F., resulted in thermally-stable nitrided electrolytic manganese containing from 5% to 6% by Weight of nitrogen, and uniformly nitrided throughout the entire charge.

Several methods may be used advantageouslytocontrol the retention time of the manganese in the reaction zone 11, such as altering the slope of the furnace tube by raising or lowering the adjustable jacks 19, but themost advantageous method of doing so is to change the rate of rotation of the furnace tube While maintaining the furnace slope constant. By adjustment of the speed re duction mechanism 25 through Which the motor 24 I tates the furnace tube, the speed of rotation may be rapidly adjusted and altered, thereby providing a simplified method for regulating the nitrogen content of the nitrided electrolytic manganese without interfering with continuous operation of the furnace.

As the nitrided electrolytic manganese leaves the reaction zone 11 it passes into the tempering zone 12, cooled by water from the spray pipes 31. The nitrided electrolytic manganese is continuously agitated while being cooled to substantially room temperature during passage through the tempering zone. The cooled nitrided manganese leaves the discharge end 13 of the furnace tube and drops through the discharge chute into a receptacle 84 or 85. By altering the direction of the deflecting plate 73, one of the receptacles may be charged while another isremoved for storage, and the gas-tight seal at the discharge end need not be disturbed. Alternatively, one receptacle may be used to collect a composite sample by periodically deflecting a little of the product into it, while the other receives the main flow of product.

The new method and apparatus has been found to be eminently suited for continuous nitriding of electrolytic manganese chips, and to have the advantage of assuring a highly uniform product-a result which is diflicult to achieve when treating material in bulk by batch methods. Very little objectionable pulverizing or grinding of the chips occurs, and at the same time no partial fusion or sintering of the chips into objectionable agglomerates occurs. A product containing 4% to nitrogen can be produced continuously at high rate, and then by reducing the rate of rotation of the furnace tube (with consequent increase in the time of retention of the metal in the hot reaction zone), and coincidentally reducing the feed rate, the nitrogen content can be increased to nearly 6%. Operation of the apparatus requires only occasional attention, and the product is substantially free of objectionable contaminants such ashydrogen and carbon.

We claim:

1. The process for continuously producing thermallystable nitrided manganese containing up to about 6% by weight of nitrogen which comprises feeding subdivided solid manganese in metallic form into a rotary nitriding vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly superatmospheric pressure, continuously rotating said vessel and thereby agitating and advancing the manganese through the vessel in contact with the flowing gaseous nitrogen, heating the manganese advancing through the vessel in contact with the gaseous nitrogen to 1750 to 1950 F. for a period sufliciently long to eflect substantially uniform nitriding of the manganese to thermally-stable nitrided form containing up to about 6% by weight of nitrogen, cooling the nitrided manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided manganese form the vessel.

2. The process for continuously producing thermallystable nitrided manganese containing up to about 6% by Weight of nitrogen which comprises feeding solid electrolytic manganese cathode chips into a rotary nitriding vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly superatmospheric pressure, continuously rotating said vessel and thereby agitating and advancing the manganese through the vessel in a direction countercurrent to the flowing gaseous nitrogen stream, heating the manganese advancing through the vessel in contact with the gaseous nitrogen to 1800 to 1850 F. for a period sufliciently long to effect substantially uniform nitriding of the manganese to thermally-stable nitriding form containing up to about 6% by weight of nitrogen, cooling the nitrided manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided manganese from the vessel.

3. The process for continuously producing thermallystable nitrided manganese containing up to about 6% by weight of nitrogen which comprises feeding subdivided solid manganese in metallic form into a rotary nitriding vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly super-atmospheric pressure, continuously rotating said vessel and thereby agitating and advancingthe manganese through the vessel in a direction countercurrent to the flowing gaseous nitrogen stream, heating the manganese advancing through the vessel in contact with the gaseous nitrogen to 1750 to 1950 F. for a period sufliciently long to effect substantially uniform nitriding of the manganese to thermally-stable nitrided form containing up to about 6% by weight of nitrogen, cooling the nitrided manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided manganese from the vessel.

4. The process for continuously producing thermallystable nitrided electrolytic manganese containing from 4% to 6% by weight of nitrogen which comprises feeding solid electrolytic manganese chips into a rotary nitriding vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly super-atmospheric pressure, continuously rotating said vessel and thereby agitating and advancing the manganese through the vessel in a direction countercurrent to the flowing gaseous nitrogen stream, heating the electrolytic manganese advancing through the vessel in contact with the gaseous nitrogen to 1750 to 1950 F. for l to 4 hours, whereby the electrolytic manganese is substantially uniformly nitrided to thermally-stable nitrided form containing from 4% to 6% by Weight of nitrogen, cooling the nitrided electrolytic manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided electrolytic manganese from the vessel.

5. The process for continuously producing thermallystable nitrided electrolytic manganese containing from 4% to 5% by weight of nitrogen which comprises feeding solid electrolytic manganese chips into a rotary reaction vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly super-atmospheric pressure, continuously rotating said vessel and thereby agitating and advancing the manganese through the vessel in a direction countercurrent to the flowing gaseous nitrogen stream, heating the manganese advancing through the vessel in contact with the gaseous nitrogen to 1750 to 1950 F. for 1 to 2 hours, whereby the electrolytic manganese is substantially uniformly nitrided to thermally-stable nitrided form containing from 4% to 5% by weight of nitrogen,

9 cooling the nitrided electrolytic manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided electrolytic manganese from the vessel.

6. The process for continuously producing thermallystable nitrided electrolytic manganese containing from to 6% by weight of nitrogen which comprises feeding solid electrolytic manganese chips into a rotary reaction vessel, introducing and maintaining a stream of gaseous nitrogen flowing through said vessel at a slightly superatinospheric pressure, continuously rotating said vessel and thereby agitating and advancing the electrolytic manganese through the vessel in a direction countercurrent to the flowing gaseous nitrogen stream, heating the electrolytic manganese advancing through the vessel in contact with the gaseous nitrogen to 1750 to 1950 F. for 2 to 4 hours, whereby the electrolytic manganese is substantially uniformly nitrided to thermally-stable nitrided form containing from 5% to 6% by weight of nitrogen, cooling the nitrided electrolytic manganese advancing through the vessel in contact with the gaseous nitrogen to substantially room temperature, and withdrawing the cooled nitrided electrolytic manganese from the vessel.

7. The process for continuously producing thermallystable nitrided electrolytic manganese containing from 4% to 6% by weight of nitrogen which comprises countercurrently contacting solid electrolytic manganese chips with a stream of gaseous nitrogen at a slightly superatmospheric pressure, continuously agitating and advancing the manganese through a reaction zone while heating the manganese in said zone in contact with the gaseous nitrogen to 1750 to 1950 F., regulating the rate of advance of the manganese through said zone so that it is retained therein for 1 to 4 hours, whereby the manganese is substantially uniformly nitrided to thermallystable nitrided form containing from 4% to 6% by weight of nitrogen, advancing the nitrided manganese through a tempering zone after its passage throughthe reaction zone, cooling the nitrided electrolytic manganese while it passes through said tempering zone in contact with the gaseous nitrogen to substantially room temperature, and then withdrawing the cooled nitrided electrolytic manganese from said tempering zone.

8. The process forcontinuously producing thermallystable nitrided electrolytic manganese containing from 4% to 6% by weight of nitrogen which comprises feeding solid electrolytic manganese chips into a substantially gas-tight rotary tube furnace having substantially gastight feed and discharge ends, a heatedreaction zone adjacentto said feed end, and a cooled tempering zone adjacent to said discharge en'd, introducing and maintaining a stream of gaseous nitrogen flowing through the furnace at a slightly superatmospheric pressure from a gas inlet adjacent to the discharge end to a gas outlet adjacent to the feed end thereof; continuously rotating said furnace tube, whereby the manganese is continuously agitated and advanced therethrough in a direction countercurrent to the flowing gaseous nitrogen stream, heating the manganese advancing through the reaction zone in contact with the gaseous nitrogen to 1750 to 1950 F. for 1 to 4 hours, whereby the manganese is substantially uniformly nitrided to thermally-stable nitrided form containing from 4% to 6% by weight of nitrogen, cooling the nitrided electrolytic manganese as it advances through the tempering zone in contact with the gaseous nitrogen to substantially room temperature, and thereafter withdrawing the cooled nitrided manganese from the discharge end from the furnace.

References Cited in the file of this patent UNITED STATES PATENTS 884,181 Machlet Apr. 7, 1908 1,914,462 Ronne June 20, 1933 2,119,528 Debuch et al. June 7, 1938 2,182,616 Juthe Dec. 5, 1939 2,305,478 Kern Dec. 15, 1942 2,307,522 Mahin Jan. 5, 1943 2,335,478 Bergman Nov. 30, 1943 2,454,020 Weitzenkorn et al. Nov. 16, 1948 2,661,963 Brown et al. Dec. 8, 1953 2,739,801 Rankin Mar. 27, 1956 2,779,584 Edvar Jan. 29, 1957 2,804,410 Wyatt et al Aug. 27, 1957 FOREIGN PATENTS 368,235 Great Britain 1932 625,390 Great Britain June 27, 1949 OTHER REFERENCES Metals and Alloys, vol. 19, April 1944, p. 859. 

1. THE PROCESS FOR CONTINUOUSLY PRODUCING THERMALLYSTABLE NITRIDED MANGANESE CONTAINING UP TO ABOUT 6% BY WEIGHT OF NITROGEN WHICH COMPRISES FEEDING SUBDIVIDED SOLID MANGANESE IN METALLIC FORM INTO A ROTARY NITRIDING VESSEL, INTRODUCING AND MAINTAINING A STREAM OF GASEOUS NITROGEN FLOWING THROUGH SAID VESSEL AT A SLIGHTLY SUPERATMOSPHERIC PRESSURE, CONTINUOUSLY ROTAING SAID VESSEL AND THEREBY AGITATING AND ADVANCING THE MANGANESE THROUGH THE VESSEL IN CONTACT WITH THE FLOWING GASEOUS NITROGEN, HEATING THE MANGANESE ADVANCING THROUGH THE VESSEL IN CONTACT WITH THE GASEOUS NITROGEN TO 1750* TO 1950*F. FOR A PERIOD SUFFICIENTLY LONG TO EFFECT SUBSTANTIALLY UNIFORM NITRIDING OF THE MANGANESE TO THERMALLY-STABLE NITRIDED FORM CONTAINING UP TO ABOUT 6% BY WEIGHT OF NITROGEN, COOLING THE NITRIDED MANGANESE ADVANCING THROUGH THE VESSEL IN CONTACT WITH THE GASEOUS NITROGEN TO SUBSTANTIALLY ROOM TEMPERATURE, AND WITHDRAWING THE COOLED NITRIDED MANGANESE FORM THE VESSEL. 